1. Field of the Invention
The present invention relates to a toner density and toner misregistration detection sensor for use in image formation of color image forming apparatuses such as a color copier and a color printer, and a color image forming apparatus using the same, and to a method for toner misregistration detection.
2. Description of the Related Art
Conventionally, a color image forming apparatus such as a color copier or a color printer is provided with a toner density detection sensor and a toner misregistration detection sensor separately. The toner density detection sensor is disclosed, for example, in Japanese Unexamined Patent Publications JP-A 9-89769 (1997), JP-A 10-62340 (1998), JP-A 10-186827 (1998), and JP-A 11-84768 (1999). The toner density detection disclosed in the publications is performed based on a difference in reflection rate resulting from irradiating toner with infrared light.
A toner misregistration detection sensor, as shown in FIG. 7A, utilizes as a light source 21 an LED in which a light pencil is narrowed by a laser or lens. The detection by the toner misregistration detection sensor is performed in such a manner that a photosensitive drum 30 is irradiated with collimated light. The photosensitive drum 30 is thereby rotated at uniform rotating speed, and reflection light reflected from each of yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (K) toner is detected by a light receiving element 22 to detect a toner misregistration by measuring time intervals between detections of the reflection light from the respective toners.
A toner misregistration sensor 20 as shown in FIG. 7A, for example, measures a time interval t1 between detection of reflection light from Y toner and detection of reflection light from K toner, a time interval t2 between detection of reflection light from M toner and detection of reflection light from K toner, and a time interval t3 between detection of reflection light from C toner and detection of reflection lights of K toner, as shown in FIG. 7B, thereby detecting Y toner, M toner, and C toner misregistrations with reference to K toner position. When the time interval t1 between the detection of the Y toner reflection light and the detection of the K toner reflection lights is longer than a predetermined value, the Y toner deviates from the K toner. When the time interval t2 between the detections of the M toner and K toner reflection lights is shorter than a predetermined value, the M toner deviates from the K toner. Furthermore, according to a difference between the time interval t1 and the time interval t2, a toner misregistration between the Y toner and the M toner can be detected. In this way, toner misregistration can be detected in accordance with differences between the time intervals between the detections of reflection light from the respective Y, M, and C toners and the detection of reflection light from the K toner.
The conventional toner density sensor detects only toner densities. Further, the conventional toner misregistration sensor detects only toner misregistrations. Therefore, in order to detect toner densities and toner misregistrations, two sensors such as a toner density sensor and a toner misregistration sensor are necessary. Therefore, there arises a problem that costs of the color image forming apparatus increases and sufficient space is necessary in the color image forming apparatus to arrange these two sensors therein.
It is an object of the invention to provide a toner misregistration detection sensor, capable of detection of both toner density and toner misregistration with a signal detected by one light emitting element and one light receiving element, a color image forming apparatus provided with the same, and a method for toner misregistration detection.
The invention relates to a toner misregistration detection sensor for use in a color image forming apparatus, comprising:
a light emitting element for irradiating a predetermined area on an object to be detected with light;
a light receiving element for receiving reflection light which is emitted from the light emitting element and reflected on a surface of the object to be detected;
toner density detection means for detection of toner density based on a signal outputted from the light receiving element; and
toner misregistration detection means for detection of toner misregistration based on a signal outputted from the light receiving element.
According to the invention, the detection functions of a toner density detection means and a toner misregistration detection means are performed based on signals from a light receiving element which receives light which is emitted from a light emitting element and is reflected on a surface of an object to be reflected. Therefore, the space occupied by the such a sensor can be smaller in comparison with that occupied with different sensors for detection of toner density and toner misregistration, with the result that cost reduction can be achieved.
In the invention, it is preferable that the toner misregistration detection means detects a misregistration of each of the yellow toner, magenta toner and cyan toner to the black toner.
According to the invention, the toner misregistration detection means utilizes the difference in the reflection rate of light between color toners such as yellow, magenta and cyan, and a black toner, thereby detecting a misregistration of each of the color toners to the black toner.
In the invention, it is preferable that the toner misregistration detection means detects a misregistration of a pattern of each of yellow toner, magenta toner and cyan toner, to a pattern of black toner.
According to the invention, the toner misregistration detection means can detect misregistration of the respective color toners to the black toner from their patterns.
In the invention, it is preferable that the toner misregistration detection means detects a misregistration of a pattern of each of yellow toner, magenta toner and cyan toner to a pattern of black toner which are placed so as to be misregistered from each other by half of a width of either of the patterns.
According to the invention, the toner misregistration detection means can detect a misregistration of a pattern of each of yellow toner, magenta toner and cyan toner to a pattern of black toner which are disposed so as to be misregistered from each other by half of a width of either of the patterns.
In the invention, it is preferable that the toner misregistration detection means detects a misregistration of a pattern of each of yellow toner, magenta toner and cyan toner to a pattern of black toner, which patterns are disposed so as to form stripes arranged at regular intervals.
According to the invention, since the toner misregistration detection means detects a misregistration of a pattern of each of yellow toner, magenta tone and cyan toner to a pattern of black toner which patterns are disposed so as to form stripes arranged at regular intervals, the toner misregistration detection means can easily detect the direction of the misregistration.
In the invention it is preferable that the toner misregistration detection means detects a misregistration of a pattern of each of yellow toner, magenta toner and cyan toner to a pattern of black toner which is disposed so as to overlap part of the pattern of each of the color toners.
According to the invention, the black toner pattern is disposed so as to overlap part of each of the color toner patterns, thus, the toner misregistration detection means can detect a misregistration of the color toner pattern to the black toner pattern.
In the invention it is preferable that the toner misregistration detection means detects a misregistration of a pattern of each of yellow toner, magenta toner and cyan toner to a pattern of black toner which is disposed so as to be partly overlapped by the pattern of each of the color toners.
According to the invention, since the black toner pattern is disposed so as to be partly overlapped by each of the color toner patterns, the toner misregistration detection means can detect misregistrations of the color toner patterns to the black toner pattern.
In the invention it is preferable that feedback of an output from the toner density detection means is carried out to an output from the toner misregistration detection means.
According to the invention, feedback of a detection result of toner density by the toner density detection means is carried out to the toner misregistration detection means, whereby toner densities of toner misregistration detection patterns can be made proper and as a result the detection by the toner misregistration detection means can be performed with high accuracy.
In the invention it is preferable that a signal processing circuit constituting the toner density detection means and the toner misregistration detection means is composed of two amplifiers, one of which is a first step amplifier using a CMOS operation amplifier and the other is a second step amplifier using a bipolar operation amplifier, and the first step amplifier is provided with a sensitivity adjustment volume.
According to the invention, the signal processing circuit constituting the toner density detection means and the toner misregistration detection means is composed of two amplifiers, one of which is a first step amplifier using a CMOS in which an output signal outputted from the light receiving element is not consumed as an input bias current and the other is a second step amplifier using a bipolar operation amplifier having a small input offset voltage. By using the two step amplifiers, an error in the signal detection circuit can be minimized. Further, the first step amplifier is provided with a sensitivity adjustment volume, thereby the variation in signals outputted from the light receiving element can be controlled.
In the invention, it is preferable that a constant voltage circuit is provided to supply standard voltages to the first step amplifier and the second step amplifier.
According to the invention, since the standard voltages of the first step amplifier and the second step amplifier are supplied from the constant voltage circuit, an influence exerted on the output from the sensor can be controlled by the variation in power voltage.
In the invention, it is preferable that the light emitting element is composed of a light-emitting diode, whose anode is connected to a driving power, and whose cathode is connected to a connector provided for controlling a current.
According to the invention, since it is possible to externally vary and control flowing current according to variation of light amount of the light-emitting element, it is possible to obtain characteristics that are not influenced by the variation of light amount of the light-emitting element.
In the invention, it is preferable that the toner misregistration detection sensor comprises:
one light emitting element for irradiating a predetermined area on an object to be detected with light; and
one light receiving element for receiving reflection of light which is emitted from the light-emitting element and is reflected by a surface of the object to be detected,
wherein axes of the elements intersect each other at a point on an object to be detected, and
wherein the light-receiving element is located at a position where a mirror reflected component of the light which is emitted from the light-emitting element and reflected by a surface of the object to be detected is not received.
According to the invention, since a light-receiving element receives only the light which is diffused and reflected by toner adhered to the object to be detected without receiving the light which is emitted from the light-emitting element and is mirror-reflected by the surface of the object to be detected, for example, in the case of employing infrared light for a light emitting element, densities of the black toner, which has low reflection rate with respect to the diffusing and reflecting light, and of the color toner, which has high reflection rate with respect to the infrared light, and a position error (a misregistration) can be detected with high accuracy.
In the invention, it is preferable that the toner misregistration detection sensor comprises:
one light emitting element for irradiating a predetermined area on an object to be detected with light; and
two light receiving elements for receiving reflection of light which is emitted from the light-emitting element and is reflected on a surface of the object to be detected,
wherein axes of the elements intersect each other at a point on an object to be detected, and
wherein one of the light-receiving elements is located at a position where a mirror reflected component of the light which is emitted from the light-emitting element and reflected on a surface of the object to be detected is not received and the other of the light-receiving elements is located at a position where a mirror reflected component of the light which is emitted from the light-emitting element and reflected on a surface of the object to be detected is received.
According to the invention, since the light-receiving element receives a light which is irradiated from the light-emitting element and is diffused and reflected or mirror reflected by toner adhered to a surface of the object to be detected, for example, in the case where toner adhered to the transfer medium (intermediate transferring body) in a black belt-shape is detected by using infrared light for a light-emitting element, densities of the color toners having high reflection rate, and of the black toner adhered to the transfer medium in a black belt-shape, and the toner misregistration can be detected with high accuracy.
The invention provides a color image forming apparatus using the toner misregistration detection sensor.
According to the invention, the color image forming apparatus is composed of the toner misregistration detection sensor, and thereby an image in which colors are well reproduced and formed without toner misregistration.
The invention provides a method for detection of toner misregistration for use in a color image forming apparatus, comprising:
disposing a pattern of a toner of each color of yellow, magenta and cyan and a pattern of black toner so as to partly overlap each other;
irradiating the patterns with light; and
detecting a misregistration of one to the other of patterns based on an amount of light received.
According to the invention, the black toner pattern and the respective color toner patterns are disposed so as to partly overlap each other, and the patterns are irradiated with light by e.g., a light emitting element. Based on the amount of light received by e.g., a light receiving element, a misregistration of one to the other of the patterns can be easily detected. Furthermore, as the light irradiated to the pattern is not used collimated light such as laser light, but light which spreads out may be used and misregistration detection can be performed using such a light, with the result that cost reduction can be achieved.